1*ae417b31SSteve Kargl.\" Copyright (c) 2026 Steven G. Kargl. 2*ae417b31SSteve Kargl.\" 3*ae417b31SSteve Kargl.\" Redistribution and use in source and binary forms, with or without 4*ae417b31SSteve Kargl.\" modification, are permitted provided that the following conditions 5*ae417b31SSteve Kargl.\" are met: 6*ae417b31SSteve Kargl.\" 1. Redistributions of source code must retain the above copyright 7*ae417b31SSteve Kargl.\" notice, this list of conditions and the following disclaimer. 8*ae417b31SSteve Kargl.\" 2. Redistributions in binary form must reproduce the above copyright 9*ae417b31SSteve Kargl.\" notice, this list of conditions and the following disclaimer in the 10*ae417b31SSteve Kargl.\" documentation and/or other materials provided with the distribution. 11*ae417b31SSteve Kargl.\" 12*ae417b31SSteve Kargl.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 13*ae417b31SSteve Kargl.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 14*ae417b31SSteve Kargl.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 15*ae417b31SSteve Kargl.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 16*ae417b31SSteve Kargl.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 17*ae417b31SSteve Kargl.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 18*ae417b31SSteve Kargl.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 19*ae417b31SSteve Kargl.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 20*ae417b31SSteve Kargl.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 21*ae417b31SSteve Kargl.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 22*ae417b31SSteve Kargl.\" SUCH DAMAGE. 23*ae417b31SSteve Kargl.\" 24*ae417b31SSteve Kargl.Dd June 5, 2026 25*ae417b31SSteve Kargl.Dt ACOSPI 3 26*ae417b31SSteve Kargl.Os 27*ae417b31SSteve Kargl.Sh NAME 28*ae417b31SSteve Kargl.Nm acospi , 29*ae417b31SSteve Kargl.Nm acospif , 30*ae417b31SSteve Kargl.Nm acospil 31*ae417b31SSteve Kargl.Nd half-cycle arc cosine functions 32*ae417b31SSteve Kargl.Sh LIBRARY 33*ae417b31SSteve Kargl.Lb libm 34*ae417b31SSteve Kargl.Sh SYNOPSIS 35*ae417b31SSteve Kargl.In math.h 36*ae417b31SSteve Kargl.Ft double 37*ae417b31SSteve Kargl.Fn acospi "double x" 38*ae417b31SSteve Kargl.Ft float 39*ae417b31SSteve Kargl.Fn acospif "float x" 40*ae417b31SSteve Kargl.Ft long double 41*ae417b31SSteve Kargl.Fn acospil "long double x" 42*ae417b31SSteve Kargl.Sh DESCRIPTION 43*ae417b31SSteve KarglThe 44*ae417b31SSteve Kargl.Fn acospi , 45*ae417b31SSteve Kargl.Fn acospif , 46*ae417b31SSteve Kargland 47*ae417b31SSteve Kargl.Fn acospil 48*ae417b31SSteve Karglfunctions compute the principal value of the arc cosine of 49*ae417b31SSteve Kargl.Fa x , 50*ae417b31SSteve Kargldivided by \*(Pi, thus measuring the angle in half-cycles. 51*ae417b31SSteve Kargl.Sh RETURN VALUES 52*ae417b31SSteve KarglThe 53*ae417b31SSteve Kargl.Fn acospi , 54*ae417b31SSteve Kargl.Fn acospif , 55*ae417b31SSteve Kargland 56*ae417b31SSteve Kargl.Fn acospil 57*ae417b31SSteve Karglfunctions return values in the range 58*ae417b31SSteve Kargl.Bk -words 59*ae417b31SSteve Kargl.Bq -1, +1 . 60*ae417b31SSteve Kargl.Ek 61*ae417b31SSteve KarglIf 62*ae417b31SSteve Kargl.Pf \&| Ns Fa x Ns \&| > 1 , 63*ae417b31SSteve Kargl.Fn acospi x 64*ae417b31SSteve Karglraise an invalid exception and returns an \*(Na. 65*ae417b31SSteve Kargl.Sh SEE ALSO 66*ae417b31SSteve Kargl.Xr asinpi 3 , 67*ae417b31SSteve Kargl.Xr atanpi 3 , 68*ae417b31SSteve Kargl.Xr acos 3 , 69*ae417b31SSteve Kargl.Xr cospi 3 , 70*ae417b31SSteve Kargl.Sh STANDARDS 71*ae417b31SSteve KarglThe 72*ae417b31SSteve Kargl.Fn acospi , 73*ae417b31SSteve Kargl.Fn acospif , 74*ae417b31SSteve Kargland 75*ae417b31SSteve Kargl.Fn acospil 76*ae417b31SSteve Karglfunctions conform to 77*ae417b31SSteve Kargl.St -isoC-2023 . 78